1. Field of the Invention
The present invention relates to a blow molding device adapted to form a blow molded article from a thermoplastic synthetic resin.
2. Description of Related Art
Conventionally, tubular blow molded articles, such as fuel tanks for use in motor vehicles, etc., have been formed of metal, but, in recent years, thermoplastic synthetic resins have been frequently used to form such tubular blow molded articles, because they can effect lightweight vehicle bodies, no rust is generated therein, and they can be readily formed into desired configurations.
In many cases, the tubular articles made of thermoplastic synthetic resins have been formed by the blow molding method, because tubular bodies can be readily formed. With the blow molding method, a parison of a molten thermoplastic synthetic resin formed into a cylindrical configuration is extruded from the upper side of a mold, and air is blown into the parison while the parison is being held with the mold, thereby forming the tubular bodies.
In this case, however, air is blown into the parison after the parison has been inflated through preblowing so that the molding cycle becomes long to degrade the productivity. In addition, when the parison is held with the mold, the parison may be stretched so that the thickness thereof may scatter, and consequently, the wall thickness of molded tubular bodies may scatter.
On the other hand, the blow molding method may be required to provide built-in parts such as valves, baffle plates adapted to restrain noise caused by the flowing of fuel, etc. in an interior of the blow molded article, such as the fuel tank.
Accordingly, in order to provide the built-in parts in the interior of the blow molded article, a device shown in FIG. 1 has been used (see published Japanese patent applications No. Hei 9-174670 and Hei 8-72129, for example.). A built-in part 10 is held in a cavity of a blow mold 12 with a holding rod 14, and a parison 16 is lowered. Then, the blow mold 12 is closed, and the parison 16 is held with pinching plates 18. Thus, the blow molded article is formed.
Where, as shown in FIG. 2, a larger-sized built-in part 20 is provided in a blow molded article, the built-in part 20 is supported with slide cores 22 in the interior of the parison 16, and then, as shown in FIG. 3. the parison 16 is closed with the pinching plates 18. At this time, as shown in FIG. 4, a lower end 24 of the parison is crushed with the pinching plates 18 into a configuration like a straight line.
As a result, as shown in FIG. 4, projecting ends of the built-in part 20 may contact an inner surface of the parison 16 to adhere to or damage the inner surface of the parison 16.